1. Field of the Invention
The present invention relates to toner used in developer for developing an electrostatic latent image in electrophotography, electrostatic recording, electrostatic printing, etc., a method of manufacturing the toner, and a process cartridge that contains the toner. More particularly, the present invention relates to toner for electrophotography used in a copying machine, a laser printer, and a fax machine for normal paper, which use a direct or indirect electrophotographic developing process, a method for manufacturing the toner, and a process cartridge that contains the toner. Moreover, the present invention relates to toner for electrophotography used in a full-color copying machine, a full-color laser printer, and a full-color fax machine for normal paper, which use a direct or indirect electrophotographic multi-color image developing process, a method for manufacturing the toner, a method for developing the toner, and a process cartridge that contains the toner.
2. Description of the Related Art
Developer used in electrophotography, electrostatic recording, electrostatic printing, etc., first adheres to an image supporter such as a photoconductor on which an electrostatic latent image is formed in a development process, then is transferred from the photoconductor to a transfer medium such as a piece of transfer paper in a transfer process, and subsequently is fixed on the surface of the transfer medium in a fixing process. Herein, a two-component developer containing carrier and toner and a one-component developer requiring no carrier (magnetic toner, non-magnetic toner) are known as developers for developing an electrostatic latent image formed on a latent image-supporting surface.
Conventionally, dry-type toner used in electrophotography, electrostatic recording, and electrostatic printing is obtained by melting and kneading a toner binder such as a styrene-based resin and a polyester, etc., with a coloring agent and by milling the obtained material.
Image quality has been improved in recent times, by reducing particle diameter of the toner. However, in the manufacturing process including normal kneading and milling, the shape of the toner particle is undefined. Also, the toner particle size is further reduced by agitation with carriers in the development part inside of an image forming apparatus, and contact stress between a development roller and a toner feeding roller and between a blade for controlling the thickness of a toner layer and a blade for frictional electrification of the photoconductor, etc., in the case of using toner as the developer in a one-component system. As a result, the image quality is lowered by formation of extremely fine particles and by the embedding of a fluidizing agent into the surface of the toner. Additionally, the fluidity of the toner as powder is reduced due to the undefined shape of the toner particles so that much energy for fluidization is required and a filling factor of putting the toner in a toner bottle is so low that miniaturization of the toner bottle cannot be sufficiently achieved. Accordingly, further reducing the particle diameter is not effective at present. Also, the presently achievable minimum of the particle diameter is being produced in the conventional milling process, so that further miniaturization of the particle diameter cannot be achieved.
Moreover, in order to create a full-color image, a transfer process for a color image created with multi-color toners from a photoconductor to a transfer medium or paper is conventionally complicated. Also, a defect in the transferred image occurs due to the deterioration of the transfer property caused by the undefined shape of the milled toner particles and the amount of the toner consumed becomes large in order to cover the defect in the transferred image. Accordingly, reducing the amount of consumption of the toner by further improvement of transfer efficiency is desired so as to obtain a high-grade image with no defects and reduce the running cost of image formation. If the transfer efficiency is very high, a cleaning unit for eliminating un-transferred toner from the surface of the photoconductor is not needed, and the advantages of miniaturization of the machine, reduction of the cost for image formation, and elimination of wasted toner can be simultaneously achieved. In order to compensate for the disadvantages of such effect of the undefined shape, various methods for manufacturing spherical toner particles have been studied.
As a method for solving those problems, methods of manufacturing toner by utilizing a suspension polymerization process and an emulsion polymerization aggregation process have been studied. Additionally, in Japanese Laid-Open Patent Application No. 7-152202, a method utilizing volume shrinkage is studied, which is called the polymer dissolution or suspension method. The method includes the steps of dispersing or dissolving a toner material into a volatile solvent such as an organic solvent with a low melting point to obtain a dispersed system or a solution, emulsifying the dispersed system or the solution in an aqueous medium that contains a dispersing agent to form droplets, and subsequently eliminating the volatile solvent from the dispersed system or the solution. The method is different from both the suspension polymerization method and the emulsion polymerization aggregation method, and many kinds of resins are available. In particular, the method has an advantage of employing a polyester resin useful for a full-color process that is required to provide enough transparency and enough smoothness to image parts after fixing. However, since used dispersing agent strongly adheres to the surface of the toner particles, elimination of the dispersing agent is difficult even by a subsequent washing process and the electrostatic property of the toner is strongly dominated by the used dispersing agent. Accordingly, average charge level of the obtained toner is low, charging speed for the toner is slow, and the toner is strongly affected by humidity.
Additionally, in Japanese Laid-Open Patent Application No. 11-149179, low-molecular resin is used for the polymer dissolving or suspending process so as to reduce the viscosity of a dispersion phase in the solution or dispersed system, to facilitate the emulsification, and to cause polymerization reaction inside the particles for improving the fixing property. However, the influence of a functional group used for the polymerization reaction inside the particles cannot be negligible. Particularly, in the case of employing an isocyanate compound, the fixing property of the toner is strongly dominated by the electrostatic property of an obtained urethane or urea group as well as the aforementioned influence of the dispersing agent.
Additionally, although it has been attempted to make a dry-type charge control agent adhere and become fixed to the surface of such obtained particles, the fixation of the toner is disturbed in many cases, so that the problem of the antinomy phenomenon of provision of electric charge to the toner and low fixation temperature of the toner has not been solved.